The effect of oxygen pressure on the rate of polypropylene oxidation determined by chemiluminescence

The chemiluminescence of non stabilized polypropylene films has been studie d at temperatures 130 and 140 degrees C at various concentrations of oxygen in the flow of oxidizing gas introduced above the polymer sample, Results have shown that the maximum level of chemiluminescence intensity is linearl y proportional to the concentration of oxygen in the gas above the sample, i.e. to the concentration of oxygen in the polymer. A kinetic model based o n a simple mechanistic scheme where the initiation of oxidation results onl y from hydroperoxide decomposition was proposed. Approximate analytical sol utions have been found in the case when k(4)k(6)/k(5)(2)much less than 1, k (4), k(5), k(6) being the termination rate constants, for, respectively (P degrees + P degrees), (P degrees + PO(2)degrees) and (PO(2)degrees PO(2)deg rees) radicals. According to this approximation, the POS concentration will be a hyperbolic function of the oxygen concentration, The experimental res ults may then be interpreted as: (1) in the conditions under study there is no sufficient oxygen concentration to scavenge all P degrees radicals, i.e . termination reactions involving these radicals are not negligible; (2) th e results are consistent with the fact that the chemiluminescence would res ult directly from hydroperoxide decomposition rather than from the POS bimo lecular termination reaction. (C) 1999 Elsevier Science Ltd. All rights res erved.